Controllable pitch propeller and drive means therefor

ABSTRACT

A controllable pitch propeller is provided in which the blades are rotatably mounted on a hollow hub having an axial bore, the wall of which is of non-circular cross-section, and control of the pitch of the blades is effected by a pair of axially-threaded nuts slidably mounted in said axial bore, and a single doublethreaded control screw threadedly connected with said nuts. The blades are mounted on the hub in a novel manner which strengthens the attachment of the blades to the hub, and permits removal or replacement of the blades without disturbing other parts involved in the assembly of the blades with the hub. A differential assembly is provided for driving the propeller and the control screw at the same speed, as well as power driven means for driving the control screw at a speed different from that of the output shaft, whereby the aforesaid nuts are moved relatively to each other without interfering with the rotation of the hub. Means are also provided for indicating the pitch position of the blades and for activating the power driven means for driving the control screw.

United States Patent 7 1 Herbert [4 1 Oct. 14, 1975 1 CONTROLL ABLE PITCH PROPELLER AND DRIVE MEANS THEREFOR William B. Herbert, lll Yantacaw Brook Road, Upper Montclair, NJ. 07043 22 Filed: Jan. 28, 1974 21 Appl. No.1 436,922

Related US. Application Data [62] Division of Ser. No. 164,502, July 21, 1971.

[76] Inventor:

[52] US. Cl. 416/160; 416/165; 416/167 [51] Int. Cl. B6311 3/02 [58] Field of Search 416/165, 163, 160, 167

[56] References Cited UNITED STATES PATENTS 2,360,982 10/1944 Sahle 416/160 X 2,501,908 3/1950 Nichols 416/160 X 2,675,084 4/1954 Nichols 416/160 2,711,796 6/1955 Amiot 416/163 FOREIGN PATENTS OR APPLICATTONS 222,581 10/1958 Australia 416/168 1,095,464 6/1955 France 416/165 885,210 8/1953 Germany 416/160 860,205 2/1961 United Kingdom.. 416/163 57,867 7/1946 Netherlands 416/165 Primary Examiner-Everette A. Powell, .1 r. Attorney, Agent, or F irmlsler and Ornstein [57] ABSTRACT A controllable pitch propeller is provided in which the blades are rotatably mounted on a hollow hub having an axial bore, the wall of which is of non-circular cross-section, and control of the pitch of the blades is effected by a pair of axially-threaded nuts slidably mounted in said axial bore, and a single doublethreaded control screw threadedly connected with said nuts. The blades are mounted on the hub in a novel manner which strengthens the attachment of the blades to the hub, and permits removal or replacement of the blades without disturbing other parts involved in the assembly of the blades with the hub. A differential assembly is provided for driving the propeller and the control screw at the same speed, as well as power driven means for driving the control screw at a speed different 'from that of the output shaft, whereby the aforesaid nuts are moved relatively to each other without interfering with the rotation of the hub. Means are also provided for indicating the pitch position of the blades and for activating the power driven means for driving the control screw.

8 Claims, 9 Drawing Figures US. Patent Oct. 14, 1975 Sheet 1 of5 3,912,416

U.S.'Patent Oct. 14, 1975 Sheet40f5 3,912,416

US. Patent Oct. 14, 1975 Sheet 5 of5 3,912,416

CONTROLLABLE PITCH PROPELLER AND DRIVE MEANS THEREFOR This is a division of application Ser. No. 164,502, filed July 21,1971.

This invention relates generally to controllable pitch propellers and to driving means therefor, but has reference more particularly to pitch controlling means and driving means for propellers used in connection with marine drive or propulsion system.

In the Gloor U.S. Pat. No. 1,396,325, a screw propeller is disclosed in which the blades are reversible relatively to the longitudinal axis of the propeller shaft, and a reversing or feathering mechanism is provided.

The propeller blades are formed at their inner ends with cylindrical stems which are mounted for rotation about their longitudinal axes in a hollow boss or hub. The stems are integral with the propeller blades, and are formed with a plurality of annular ribs, so that in assembling the blades with the hub, it is necessary to make the intermediate externally cylindrical section of the hub in two parts and to provide bolts for connecting said parts to each other.

From each stern a pair of parallel pins project eccentrically into adjacent slides movable in grooves or recesses of separately movable wings. These wings are so disposed relatively to each other as to slidably engage or interengage with one another.

The wings are mounted on the ends of members which project into the hollow boss or hub, and by moving such members longitudinally in opposite directions, the slides within the grooves or recesses of the corresponding wings will move transversely of the wings, and the propeller blades will be turned about their longitudinal axes, thereby reversing or feathering the blades.

One of the aforesaid members is a tubular member mounted for longitudinal movement in a hollow portion of the main propeller shaft, and the other member is a solid rod mounted for longitudinal movement inside the first or tubular member, both members being thus concentric with and adapted to revolve with the propeller shaft.

Due to the fact that one of said members slides inside the other, there is constant friction therebetween, as well as between parts of the mechanism which causes relative longitudinal movement of said members, including collars, spokes and disks. In other words, the forces necessary to either rotate the propeller blades or prevent them from rotating, must necessarily be carried up to the control handle or lever to obtain or to hold the position of the blade, and this has been found to be highly disadvantageous in a controllable pitch propeller.

The present invention has as its primary object, the provision of a controllable pitch propeller which overcomes all of the disadvantages of the mechanism disclosed in the aforesaid Gloor patent.

Another object of the invention is to provide a controllable pitch propeller in which the propeller blades are attached to the intermediate externally cylindrical section of the hub in such a manner that the intermediate section of the hub can be made in one part, instead of two parts, thereby reducing costs, and dispensing with the need for bolts or other fasteners for connecting the two parts.

Another object of the invention is to provide a controllable pitch propeller of the character described, in which the intermediate externally cylindrical section of the hub is provided with an internal cavity for the reception of pitch operating nuts, the wall of which cavity is of non-circular, i.e., of triangular or polygonal crosssection, in contrast to a cavity of circular cross-section, whereby the size of the propeller blade stems, pitch operating nuts and other internal parts may be increased for a given size of hub, with corresponding increase in strength of such parts.

Another object of the invention is to provide a controllable pitch propeller of the character described, which is characterized by the use of a single screw shaft or rod for actuating pitch operating nuts, whereby all of the forces involved in rotating the blades to control the pitch of the latter, are completely confined to the internal threads in the pitch operating nuts, and within a relatively short length or section of said screw shaft or rod.

A further object of the invention is to provide a controllable pitch propeller and operating mechanism therefor, in which frictional resistance between parts is reduced to a minimum, and assembly of the parts is greately facilitated or simplified.

A still further object of the invention is to provide a novel double differential device for the controllable pitch propeller, which enables the pitch of the propeller blades to be controlled while the propeller and driving means therefor are rotating.

Other objects and advantages of my invention will be apparent during the course of the following description.

In the accompanying drawings forming a part of this specification, and in which like numerals are employed to designate like parts throughout the same,

FIG. 1 is a fragmentary schematic or diagrammatic view showing the controllable pitch propeller system, embodying the invention;

FIG. 2 is a view, partly in elevation and partly in section, showing a controllable pitch propeller and a portion of the operating mechanism therefor;

FIG. 3 is a view, partly in elevation and partly in section, showing the other portion of the operating mechanism, including the double differential device;

FIG. 4 is a view, partly in cross-section and partly in elevation, showing the pitch operating nuts in an advanced position relatively to each other;

FIG. 5 is a view similar to FIG. 4, but showing the pitch operating nuts in a retracted position relatively to each other;

FIG. 6 is a fragmentary cross-sectional view, taken on the line 6-6 of FIG. 4, but showing portions of the propeller blades and the manner of attachment of the blades to the blade roots;

FIG. 7 is a view showing the pitch operating nuts and control screw therefor, independently of the propeller;

FIG. 8 is a cross-sectional view, taken on the line 8-8 of FIG. 7, and

FIG. 9 is a cross-sectional view, taken. on the line 99 of FIG. 7.

Referring more particularly to the drawings, and especially to FIG. I, there is illustrated, in somewhat diagrammatic or schematic fashion, the aft portion 10 of a boat, a propeller 11, a propeller drive shaft 12, a V- drive 13 for the propeller shaft, an engine 14 for the V- drive, a double differential device 15 for controlling the pitch of the blades of the propeller 11, and means for indicating the position of the propeller blades and for activating the control mechanism.

The propeller 11 comprises a tubular hub 16 having a cylindrical outer surface 17 and an axial cavity or bore defined by fiat surfaces or sides- 18, 19 and 20, a diametric cross-section through this cavity or bore being in the form of an equilateral triangle. It is to be understood, in this connection, that the number of surfaces defining this axial cavity or bore will correspond to the number of propeller blades of the propeller, which, in this instance, is a three-bladed propeller. Thus, in a four-bladed propeller, the number of surfaces or sides would be four; in a five-bladed propeller, the number of surfaces or sides would be five. In a twobladed propeller, the cavity would be square or rectan gular in cross-section.

Extending radially through the wall of the hub 16, from the surfaces 18, 19 and 20, to the surface 17, are circumferentially spaced bores 21, 22 and 23 (see FIG. 6), these bores having annular grooves or recesses 24 of V-shaped cross-section in the walls thereof adjacent their radially-outer ends, for a purpose to be presently described.

The number of such radial bores, shown in this instance as three, corresponds with the number of propeller blades, so that it is to be understood that the number of bores is not limited in respect to this invention.

Secured to the rear end of the hub 16, as by means of socket head screws 25, is a conical cap 26.

The hub 16, in turn, is secured as by means of socket head screws 27, to the driven section 28 of the hollow or tubular propeller shaft 12.

The driven section 28 of the propeller shaft is connected, by screws 29, to a collar 30, which is connected, as by screws 31, to a second collar 32. The collar 32 is connected, as by screws 33, to a tubular output shaft 34, which is a part of the V-drive 13. The output shaft 34 is mounted for rotation in bearings 35 and 36 mounted in axially-aligned openings 37 and and 38 respectively of the housing 39 of the \/-drive 13. The bearings 35 and 36 are retained against displacement by cover plates 40 and 41 secured to the housing 39.

The V-drive 13 includes a bevel pinion 42, which drives a bevel gear 43, which, in turn, drives the output shaft 34 of the V-drive.

The propeller, in this case, comprises three circumferentially-spaced blades 44, 45 and 46 of identical construction.

Each blade is secured, as by means of four circumferentially-spaced cap screws 47, to a conical blade base 48 disposed in the outer end of the bore 21, 22 or 23. The blade base is provided with circumferentiallyspaced unthreaded openings 50 for passage therethrough of the screws 47. The screws 47 are threadedly secured to an annular blade root 51 disposed in the inner end of the bore 21, 22 or 23, and having a conical portion 52. The blade root 51-52 is provided with threaded openings 53 for receiving the ends of the screws 47.

For the purpose of securing the blade base 48 to the blade root 51-52, prior to attachment of the blade to the blade base and blade root, a socket head screw 54 is provided, which extends through an unthreaded central opening 55 in the blade base 48, and is threaded into a threaded opening 56 of the blade root. The blade 44 is provided with a central hole 57 into which the head of the screw 54 extends when the blade is secured to the blade base and blade root.

For the purpose of aligning the openings 50 with the openings 53, when assembling the blade base and blade root, a dowel pin 58 is provided, which extends into the blade base and blade root, and locates these parts in proper circumferential relationship to each other for assembly.

The blade base 48 and conical portion 52 of the blade root 51 respectively coact with the annular grooves or recesses 24 to confine therebetween a bearing 59, which may be bearing rollers, bearing balls or nonrolling segments of a ring, which results in a plaing bearing mounting instead of an anti-friction bearing.

The aforesaid method of connecting the blades to the blade roots, strengthens the attachment of the blades to the blade bases and to the blade roots and provides proper load to bearing surfaces for the bearing rollers. This method of anchoring the blades also permits removal and/or replacement of a blade without disturbing the other parts involved in the assembly.

Each blade root 51 has mounted in its inner end a pair of rotatable pins 60 and 61 spaced from each other diametrically of the inner face of the blade root, and respectively provided with a rectangular slide block 60a and 610 formed integrally with the pin.

Mounted for slidable axial movement in the axial cavity or bore of the hub 16 is a pair of nuts 62 and 63 for controlling the pitch of the propeller blades.

The nut 62 has a triangular portion 64 conforming in contour to the axial cavity or bore of the hub 16, and having a threaded axial bore 65 extending therethrough, while the nut 63 has a similar triangular portion 66 conforming in contour to the axial cavity or bore of the hub 16, and having a threaded axial bore 67 extending therethrough, which is of slightly larger diameter than the bore 65 and the threads of which are of opposite hand to the threads of the bore 65.

The portion 64 of the nut 62 is provided with fingers or extensions 68, 69 and 70, spaced circumferentially about the axis of the bore 65, and extending from the inner face of the portion 64 (see FIGS. 7 and 8), and are of the contour shown in FIG. 8. The fingers or extensions 68, 69 and are provided respectively in one face thereof with slots or grooves 68a, 69a and 7011, these slots or grooves lying in a common plane transversely of the nut 62.

The portion 66 of the nut 63 is similarly provided with fingers or extensions 71, 72 and 73, spaced circumferentially about the axis of the bore 67, and extending from the inner face of the portion 64 (see FIGS. 7 and 9), and are of the contour shown in FIG. 9.

The fingers or extensions 71, 72 and 73 are arranged or spaced circumferentially to alternate with the fingers or extensions 68, 69 and 70, so that when the nuts are in the position shown in FIGS. 4, 5 and 6, the fingers 71, 72 and 73 extend into and fill the spaces between the fingers 68, 69 and 70 and slide along the latter fingers. The fingers 71, 72 and 73 are provided respectively in one face thereof with slots or grooves 71a, 72a and 73a, these slots or grooves lying in a common plane transversely of the nut 63.

As seen in FIGS. 4, 5 and 6, the block 60a of the blade root 51 of the blade 44 lies in the slot or groove 69a of the finger 69, while the block 61a of that blade root lies in the slot or groove 71a of the finger 71. As seen in FIG. 6, the block 60a of the blade root 51 of the blade 45 lies in the slot or groove 68a of the finger 68,

while the block 61a of that blade root lies in the slot or groove 72a of the finger 72, and the block 60a of the blade root 51 of the blade 46 lies in the slot or groove 70a of the finger 70, while the block 61a of that blade root lies in the slot or groove 73a of the finger 73.

For the purpose of moving the nuts 62 and 63 toward and away from each other, a control screw 74 is provided having threads 75, which are in threaded engagement with the threads of the bore 67 in the nut 63, and threads 76 which are in threaded engagement with the threads of the bore 65 in the nut 62. Since the threads of the bore 67 are of opposite hand to those of the threads in the bore 65, it follows that rotation of the control screw 74 in one direction will cause the nuts 62 and 63 to move away from each other, and that rotation of the control screw 74 in the opposite direction will cause the nuts 62 and 63 to move toward each other. Such movement of the nuts away from each other, that is to say, from the position shown in FIG. 4 to that shown in FIG. 5, will cause the blocks 60a and 61a to move from the position shown in FIG. 4 to that shown in HO. 5, and the other sets of blocks to move correspondingly, thereby causing the propeller blades to be rotated about their longitudinal axes in an obvious manner, for controlling the pitch of the blades.

The control screw 74 is keyed to a coupling member 77, which is interlocked with a coupling member 78. This coupling may, for example, be a Boston coupling No. FCBBlS.

The coupling member 78 is secured to the after end of a control shaft 79, which is mounted for rotation in radial thrust bearings 80 and 81 mounted in the driven section 28 of the propeller shaft. The bearing 80 is retained against axial displacement relatively to the driven section 28 by means of a snap ring 83 secured to the shaft 79 adjacent the bearing 80.

Rearwardly of the bearing 81, the shaft 79 is of re duced diameter, this portion being designated by reference numeral 79a, and referred to hereinafter the control shaft.

The control shaft 79:: extends axially through the output shaft 34 and into a differential assembly to be presentlydescribed, a portion 79b of this control shaft intermediate its ends being threaded for a purpose to be also presently described.

For the purpose of controlling the circumferential position of the control shaft 79a relatively to that of the output shaft 34, and thereby controlling the pitch of the propeller blades, a differential device is provided, which is rigidly supported by bracket arms or bars 83 and 84 extending from the housing of the V-drive 13, andwhich is housed within a housing 85 provided with end plates 86 and 87, this housing having a motor 88 mounted thereon.

This differential device comprises a planetary carrier 89, mounted for rotation in the end plate 87, and adapted to be driven at such times that the pitch of the propeller blades is to be changed, by the motor 88 through the intermediary of idler mechanism 90 and a suitable belt, gear or worm reduction, indicated generally by reference numeral 91.

The carrier 89 carries cantilever supports 92 for bearing shafts 93 and 94.

The differential device further includes a flanged member 95 mounted for rotation in the end plate 86 and normally driven by guide rods 96 and 97 extending from the output shaft 34. The member 95 is pinned to a bevel gear 98, which drives a bevel gear 99 mounted for rotation about a stationary bearing shaft 100 affixed to the housing 85. The gear 99, in turn, drives bevel gears 101 and 102 which idle on the control shaft 79a. The gears 101 and 102 are rigidly interconnected as a unit by a pin 103, and the gear 102 drives bevel gears 104 and 105, which are rotatably mounted on bearing shafts 93 and 94 respectively.

The bevel gears 104 and 105 are in driving engagement with a bevel gear 106, which is keyed to the control shaft 79a, and which is rotatable relatively to the planetary carrier 89.

Means have also been provided, generally designated hereinbefore by reference numeral 15a, for achieving the dual function of activating the motor 88 and indicating visually the position or pitch setting of the propeller blades.

Such means includes the guide rods 96 and 97, to which reference has previously been made, and comprises an axially movable disk 107 for which the rods 96 and 97 serve as guides, a sliding bearing 108 sup ported on a stationary support 109, and operating block 110, switches 111 and 112 carried by the block and provided with actuating buttons, operating arms 113 and 114 carried by the bearing 108, and rollers 115 and 116 revolubly supported by the upper ends of the arms 113 and 114 respectively, and adapted to engage the opposite faces of the disk 107.

The block 110 is positioned along the bearing 108 by means of any suitable remote control device such, for example, as a flexible push-pull cable (not shown).

When the pitch of the propeller blades is not to be changed, the motor 88 is not energized, and consequently, the output shaft 34 drives the guide rods 96 and 97, member 95, bevel gears 98, 99, 101, 102, 104 and 105, and the control shaft 790, the planetary carrier 89 remaining motionless. The output shaft 34 and control shaft 79a therefore rotate at the same or identical speed, and, consequently, no pitch change will take place in the propeller. The effect, in other words, is tantamount to having the output shaft, control shaft and nuts 62 and 63 locked together as a unit. At the same time, the disk 107, although rotated by the guide rods 96 and 97, will not be moved axially, even though it is in threaded engagement with the control shaft 79a.

With the propeller either rotating or at rest, the lever arms 113 and 114 are held together by a spring 117, with the rollers 115 and 116 in contact with the disk 107. When the pitch of the propeller blades is to be changed, movement of the operating block 110 to the left, as viewed in FIG. 3, will cause the disk 107 to interfere with free movement of the roller 116, thereby displacing lever 114 and removing pressure from the switch 112, closing the control circuit to motor 28, thus rotating the planetary carrier.

Rotation of the planetary carrier 89 causes rotation of the control shaft 79a at a speed different from that of the output shaft 34, thereby changing the pitch setting of the propeller blades. As the pitch changes, disk 107 will move along the shaft 79a to the left, allowing spring 117 to return lever 114 to its normal position. In this position, lever 114 depresses the actuating button of switch 112, opening the circuit to motor 88, and resulting in the cessation of the pitch changing movement. Movement of the block 110 to the right will result in a similar cycle, but in the opposite direction.

In either case, the disk 107 moves a distance corresponding to the distance through which the block 110 has been moved, and the position of the disk, at such time, will indicate visually the position or pitch setting of the propeller blades.

The function of the differential assembly, which has been described, is to enable this control operation to take place while the propeller and the complete drive train therefor are rotating.

It is to be noted, in particular, that the entire pitch control or feathering action is confined within the relatively short length of the hub 16, through the medium of a single double-threaded, control screw 74, which is also located within the hub. The forces involved in rotating the propeller blades for pitch control or for resisting rotation of the propeller blades by external forces are, accordingly, completely confined to the internal threads in the pitch operating nuts, and to a relatively short section or length of the control screw.

This arrangement represents a marked improvement over that disclosed in the Gloor patent, in that it eliminates all of the disadvantages of the Gloor patent to which reference has been made, and provides an operating mechanism in which frictional resistance between paarts is reduced to a minimum, and assembly 'of the parts is greatly simplified.

The threaded axial bores 65 and 67 of the nuts 62 and 63, as well as the portions 75 and 76 of the control screw 74 need not be of different diameters, and may be of the same diameter. Moreover, the use of a control screw 74 which is independent of the coupling 7778 enables the nuts 62 and 63 to be assembled from either end with the control screw before the coupling is installed.

Another advantage of the present invention resides in the fact that the propeller blades are attached to the intermediate externally-cylindrical section of the hub in such a manner that this section of the hub can be made in one part, instead of two parts, as in Gloor, thereby reducing cost, and dispensing with the need for bolts or other fasteners for connecting the two parts.

Another advantage resides in the fact that blade bases and blade roots are utilized in assembling the propeller blades with the hub, so that the method of connecting the blades to the blade roots strengthens the attachment of the blades to the blade bases and to the blade roots and provides proper load to bearing surfaces for the bearing rollers or other bearing means utilized. It also permits removal and/or replacement of a blade without disturbing the other parts involved in the assembly.

The use of a propeller hub having an internal cavity for the reception of the pitch controlling nuts, the wall of which is of triangular or polygonal cross-section permits the size of the propeller blade stems, pitch controlling nuts, and other internal parts to be increased for a given size of hub, with corresponding increase in the strength of such parts.

The use of the double differential assembly enables the propeller pitch settings to be controlled through power driven means, and while the propeller and the complete drive train therefor are rotating.

The use of the indicator disk and switches provides a convenient method of indicating visually the position or pitch setting of the propeller blades, as well as activating the motor.

It is to be understood that the form of my invention, herewith shown and described, is to be taken as a preferred example of the same, and that various changes may be made in the shape, size and arrangement of parts thereof, without departing from the spirit of the invention or the scope of the subjoined claims.

I claim:

1. In a controllable pitch propeller, a hub having blades mounted thereon for rotation about axes extending radially to said hub, a pair of nuts mounted in said hub for slidable axial movement relatively to each other in said hub, means responsive to said axial movement for rotating said blades, a control screw extending axially through said nuts, said control screw having a threaded portion in threaded engagement with one of said nuts and an oppositely threaded portion in threaded engagement with the other of said nuts, an output shaft for driving said hub, means for rotating said screw independent of the RPM of said output shaft, a differential assembly for driving said screw rotating means at the same speed as said output shaft, and guide rod means interconnecting said output shaft and said differential.

2. A controllable pitch propeller, as defined in claim 1, including power-driven means for driving said screw rotating means at a speed different from that of said output shaft, whereby said pitch controlling nuts are moved relatively to each other without interfering with the rotation of said hub.

3. A controllable pitch propeller, as defined in claim 2, including means for indicating the pitch position of the blades and for activating said power-driven means.

4. A controllable pitch propeller, as defined in claim 3, wherein said indicating means comprises a disk slidable along said guide rods and in threaded engagement with said screw rotating means.

5. A controllable pitch propeller, as defined in claim 1, including power-driven means for driving said Control screw at a speed different from that of said output shaft, whereby said first-named means are actuated without interfering with the rotation of said hub.

6. A controllable pitch propeller, as defined in claim 5, including means for indicating the pitch position of the blades and for activating said power-driven means.

7. A controllable pitch propeller, as defined in claim 6, wherein said output shaft and differential assembly are interconnected by means of guide rods, and said indicating means comprises a disk slidable along said guide rods and in threaded engagement with said screw rotating means.

8. [n a controllable pitch propeller system including an engine, a controllable pitch propeller, drive shaft means interconnecting said engine and said propeller, the combination comprising a hub having blades adjustably mounted thereon for rotation about axes extending radially to said hub, blade adjusting means mounted in said hub for rotating said blades, control means'for varying the pitch of said propeller within a predetermined constant time frame in all modes of operation including a control shaft connected to said blade adjusting means, said control shaft normally rotating at the same speed as the drive shaft interconnecting said engine and said propeller and maintaining the selected propeller pitch, said control means further including actuating means for rotating said control shaft relative to said drive means including a double differential assembly isolated from the torque generated by the and drive said control shaft only at a speed differing from said drive shaft interconnecting said engine and said propeller and thus varying the pitch of said propeller blades. 

1. In a controllable pitch propeller, a hub having blades mounted thereon for rotation about axes extending radially to said hub, a pair of nuts mounted in said hub for slidable axial movement relatively to each other in said hub, means responsive to said axial movement for rotating said blades, a control screw extending axially through said nuts, said control screw having a threaded portion in threaded engagement with one of said nuts and an oppositely threaded portion in threaded engagement with the other of said nuts, an output shaft for driving said hub, means for rotating said screw independent of the RPM of said output shaft, a differential assembly for driving said screw rotating means at the same speed as said output shaft, and guide rod means interconnecting said output shaft and said differential.
 2. A controllable pitch propeller, as defined in claim 1, including power-driven means for driving said screw rotating means at a speed different from that of said output shaft, whereby said pitch controlling nuts are moved relatively to each other without interfering with the rotation of said hub.
 3. A controllable pitch propeller, as defined in claim 2, including means for indicating the pitch position of the blades and for activating said power-driven means.
 4. A controllable pitch propeller, as defined in claim 3, wherein said indicating means comprises a disk slidable along said guide rods and in threaded engagement with said screw rotating means.
 5. A controllable pitch propeller, as defined in claim 1, including power-driven means for driving said control screw at a speed different from that of said output shaft, whereby said first-named means are actuated without interfering with the rotation of said hub.
 6. A controllable pitch propeller, as defined in claim 5, including means for indicating the pitch position of the blades and for activating said power-driven means.
 7. A controllable pitch propeller, as defined in claim 6, wherein sAid output shaft and differential assembly are interconnected by means of guide rods, and said indicating means comprises a disk slidable along said guide rods and in threaded engagement with said screw rotating means.
 8. In a controllable pitch propeller system including an engine, a controllable pitch propeller, drive shaft means interconnecting said engine and said propeller, the combination comprising a hub having blades adjustably mounted thereon for rotation about axes extending radially to said hub, blade adjusting means mounted in said hub for rotating said blades, control means for varying the pitch of said propeller within a predetermined constant time frame in all modes of operation including a control shaft connected to said blade adjusting means, said control shaft normally rotating at the same speed as the drive shaft interconnecting said engine and said propeller and maintaining the selected propeller pitch, said control means further including actuating means for rotating said control shaft relative to said drive means including a double differential assembly isolated from the torque generated by the drive means interconnecting said engine and said propeller and operatively connected to said control shaft for selectively driving said control shaft at a differing speed relative to said drive shaft for said propeller, said actuating means being normally at rest and selectively operable to drive one input to said double differential and drive said control shaft only at a speed differing from said drive shaft interconnecting said engine and said propeller and thus varying the pitch of said propeller blades. 